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https://issues.apache.org/jira/browse/CASSANDRA-15430?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17017955#comment-17017955
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Thomas Steinmaurer commented on CASSANDRA-15430:
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[~benedict], as discussed, a few more JFR-based screens to better show the
differences, until you find time to open JFR files yourself. Again, it is all
about the write path (only) executing batch messages. Both had the same *JFR
duration*, namely *15min*.
Cassandra *2.1.18*:
* BatchMessage.execute - In total: 42,76 GByte with next level top contributors:
** BatchStatement.getMutations => 19,46 GByte
** BatchStatement.executeWithoutConditions => 16,97 GByte
!screenshot-1.png!
Cassandra *3.0.18*:
* BatchMessage.execute - In total: 451,86 GByte (factor 10 more) with next
level top contributors:
** BatchStatement.executeWithoutConditions => 214,23 GByte
** BatchStatement.getMutations => 205,52 GByte
For *3.0.18*, more in-depth drill-down for
BatchMessage.executeWithoutConditions (214,23 GByte)
!screenshot-2.png!
resp.: BatchMessage.getMutations (205,52 GByte)
!screenshot-3.png!
A bit hard to give sufficient details with screen shots, so likely it would be
simply the best option, to work directly with the provided JFR files.
Thanks a lot!
> Cassandra 3.0.18: BatchMessage.execute - 10x more on-heap allocations
> compared to 2.1.18
> ----------------------------------------------------------------------------------------
>
> Key: CASSANDRA-15430
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15430
> Project: Cassandra
> Issue Type: Bug
> Reporter: Thomas Steinmaurer
> Priority: Normal
> Attachments: dashboard.png, jfr_allocations.png, mutation_stage.png,
> screenshot-1.png, screenshot-2.png, screenshot-3.png
>
>
> In a 6 node loadtest cluster, we have been running with 2.1.18 a certain
> production-like workload constantly and sufficiently. After upgrading one
> node to 3.0.18 (remaining 5 still on 2.1.18 after we have seen that sort of
> regression described below), 3.0.18 is showing increased CPU usage, increase
> GC, high mutation stage pending tasks, dropped mutation messages ...
> Some spec. All 6 nodes equally sized:
> * Bare metal, 32 physical cores, 512G RAM
> * Xmx31G, G1, max pause millis = 2000ms
> * cassandra.yaml basically unchanged, thus same settings in regard to number
> of threads, compaction throttling etc.
> Following dashboard shows highlighted areas (CPU, suspension) with metrics
> for all 6 nodes and the one outlier being the node upgraded to Cassandra
> 3.0.18.
> !dashboard.png|width=1280!
> Additionally we see a large increase on pending tasks in the mutation stage
> after the upgrade:
> !mutation_stage.png!
> And dropped mutation messages, also confirmed in the Cassandra log:
> {noformat}
> INFO [ScheduledTasks:1] 2019-11-15 08:24:24,780 MessagingService.java:1022 -
> MUTATION messages were dropped in last 5000 ms: 41552 for internal timeout
> and 0 for cross node timeout
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,157 StatusLogger.java:52 - Pool
> Name Active Pending Completed Blocked All Time
> Blocked
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,168 StatusLogger.java:56 -
> MutationStage 256 81824 3360532756 0
> 0
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,168 StatusLogger.java:56 -
> ViewMutationStage 0 0 0 0
> 0
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,168 StatusLogger.java:56 -
> ReadStage 0 0 62862266 0
> 0
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,169 StatusLogger.java:56 -
> RequestResponseStage 0 0 2176659856 0
> 0
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,169 StatusLogger.java:56 -
> ReadRepairStage 0 0 0 0
> 0
> INFO [ScheduledTasks:1] 2019-11-15 08:24:25,169 StatusLogger.java:56 -
> CounterMutationStage 0 0 0 0
> 0
> ...
> {noformat}
> Judging from a 15min JFR session for both, 3.0.18 and 2.1.18 on a different
> node, high-level, it looks like the code path underneath
> {{BatchMessage.execute}} is producing ~ 10x more on-heap allocations in
> 3.0.18 compared to 2.1.18.
> !jfr_allocations.png!
> Left => 3.0.18
> Right => 2.1.18
> JFRs zipped are exceeding the 60MB limit to directly attach to the ticket. I
> can upload them, if there is another destination available.
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